This invention relates to a method of polymerization particularly in the process of polymerization where the reactions are highly exothermic and the viscosity of the reaction mixture increases greatly at an early stage in the reaction, thus leading to a problem in heat transfer which in turn results in difficulties in control which are manifested by the development of hot spots in the reactor. The ultimate result is gellation of the polymer which in turn causes excessive fouling of the reactor.
Broad disclosures of methods of preparing conventional elastomers, in particular butyl rubbers, may be found in U.S. Pat. No. 2,513,820; 2,529,530; 2,582,411; 2,583,240 and 2,683,138.
Sparks and Garber disclose a polymerization process for the preparation of butyl rubber in their U.S. Pat. No. 2,529,520 which comprises using as the vehicle a mixed solvent phase comprising a blend of a non-solvent and a solvent for the polymer.
Illustrative examples of non-solvents for their process are methyl chloride and ethyl chloride. Illustrative of examples of solvents are butane and pentane. The monomers are completely soluble in the solvent-non-solvent system whereas the polymer is only soluble in the solvent portion of the vehicle.
If a proper adjustment is made with respect to the amount of non-solvent, olefin to be polymerized and the solvent, a solid polymer can be produced which is "solvated" sufficiently to destroy its adhesive power, but is not in solution to such an extent as to raise the viscosity of the system unduly. Accordingly, polymerization may be conducted to any desired extent without yielding a mixture which is too viscous to flow or handle and at the same time the stickiness and adhesiveness of the polymer are so slight that it is readily removed from the reactor walls and stirring equipment merely by the agitation ordinarily produced by the conventional stirrer.
In effect, the polymerization system comprises a bulk non-solvent vehicle having dispersed therein particles of polymer into which solvent has been dissolved such that the solvent-polymer mixture is readily broken up into smaller particles by agitation and are sufficiently solvated so as to avoid agglomeration of the particles.
U.S. application Ser. No. 550,649, incorporated herein by reference discloses certain flowable polymers of this invention prepared in a diluent which includes saturated straight chain, branched chain and cyclic aliphatic hydrocarbons having from 4-8 carbon atoms. Aromatic material such as benzene and toluene are also used. These solvents are solvents for the polymers and the polymerization carried out is characterized as "solution polymerization". Such a solution polymerization has disadvantages resulting from the combination of (1) high viscosity of the solution-polymer system and (2) poor heat transfer characteristics resulting from the high viscosity and from the rapid fouling.
Conventional techniques to produce copolymers of isoolefins and diolefins such as butyl utilize "slurry-polymerization" type of processes in which a non-solvent for the polymer is used as a diluent. However, this type of process has drawbacks when the product to be produced is the low molecular weight flowable viscous polymers of this invention. At the polymerization temperatures, i.e. -30 to -80.degree.C., the slurry particles are sticky particles which immediately agglomerate and readily adhere to reactor heat transfer surfaces resulting in complete mass fouling of the reactor.